Transmitted in "Purple," the highest security Japanese diplomatic code (which we had been reading for a very long time), it may have been read in high-level Washington even before it was by the ambassador. No one in Washington thought it important enough to relay to Hawaii.
Ed Layton and Joe Rochefort took no Sunday ease on Oahu beaches. Intelligence chief Layton pored again and again over information from across the Pacific. Jap carrier divisions 1 and 2 were still no where to be found. Rochefort's and his cryptographers, still trying to make useful sense of the Japanese naval code JN25, made no important breakthroughs and were forced to use the crudest form of SigInt (signals intelligence) -- guessing based on what little of the code they had broken, primarily radio direction finding on the (almost) enemy ships whose call signs they knew.
Pearl Harbor code breakers had been forbidden by Washington to read Purple code. In the Philippines, MacArthur had the necessary machines and could read it at will.
Still far to the north, but getting closer, Communications Officer Kazuiyoshi Koichi of the Hiel was having an uncomfortable time of it. Kudo Butai meteorologists had it wrong yesterday, and Sunday's weather was miserable. Besides, he was sleeping badly on his wooden box pillow full of vital radio parts from the battle cruiser's transmitters. From Yamamoto himself had come the order: Strict radio silence until after curtain rise, one week from today.